1. Field of the Invention:
The present invention relates to sliding-vane rotary compressors, and more particularly to a sliding-vane rotary compressor having a variable capacity which is suitable for use in an automotive air conditioning system.
2. Related Art:
Sliding-vane rotary compressors are known in which vanes are slidably carried in radial slots in a rotor disposed in a bore of a cylinder and, as the rotor is rotated by an automotive engine, they slide on the inner wall of the bore to compress a fluid trapped between adjacent vanes. An advantage of the sliding-vane rotary compressors over the reciprocating compressors lies in a high volumetric efficiency. However, the rotary compressors is disadvantageous in that the volumetric efficiency increases with an increase in engine r.p.m., while the refrigerating capacity drops slightly. Because of such peculiar properties, the rotary compressors perform a large displacement volume operation when the engine r.p.m. is high. This operation would cause various difficulties such as, for example, an undue increase in pressure of the discharged refrigerant gas, an uncomfortable room condition due to temperature fluctuation of fresh air caused by a repeated activation and de-activation of an electromagnetic clutch, and a notable power loss due to imbalance in capacity between the compressor, an evaporator and a condenser in an air conditioning system.
Japanese Patent Laid-open Publication No. 57-91394 discloses one prior attempt taken to overcome the foregoing difficulties, wherein an intake pressure control valve is provided for adjusting the capacity of a sliding-vane rotary compressor. The control valve is actuatable in response to the pressure in a low pressure chamber in the compressor so as to reduce the flow of a refrigerant gas when the pressure of the refrigerant gas drops below a predetermined value, thereby enabling the compressor to operate at a reduced displacement volume. According to the disclosed arrangement, the control valve includes a valve body disposed in a bore extending in a compressor body perpendicularly to an intake opening through which a compression chamber, while in the intake stage, communicates with the low pressure chamber. The valve body is biased by a spring and adapted to move into and out of an intake passage to directly control the pressure in the intake passage. The control valve thus constructed is however unable to create a valve-activating force strong enough to move the valve body for throttling the flow of the refrigerant gas. Another drawback is in that the control valve is less responsive to the pressure change and hence difficult to control with accuracy.